Purification and characterization of a novel bacteriocin produced by Enterococcus faecalis CG-9 from human saliva

Enhanced production of bacteriocin by Bacillus subtilis ZY05

Bacteriocin-producing strains were isolated from the soil of the rice field, screened out using an agar-well diffusion assay against six indicator bacterial strains, and the highest among them was selected for further investigation. The study focuses on how different growing conditions affect bacteriocin production. One-parameter-at-a-time (OPAT) and a central composite design of response surface methodology (RSM) were used to perform the optimization in two steps. In the OPAT trials, bacteriocin synthesis was elevated by 29%, 45%, and 34%, by employing sucrose as a carbon source and changing the NaCl concentration and pH at 7, respectively. To determine the linear, squared, and interaction correlations among the process variables to predict the ideal conditions for production, a four-factor central composite design (CCD) of RSM was used. It was determined that the analysis of variance (ANOVA), which produces a recognized model using RSM, is sufficient to describe bacteriocin production regarding activity (R2 = 0.9606). The ideal conditions for increased production were 1.51% sucrose concentration, 1.59% NaCl concentration, pH 6.35, and 28.66 (about 29) hours of incubation. The value predicted by RSM (4051.55 AU/mL) was approximately two times greater than the value of a non-optimized medium. The experimental value of 4403.85 AU/mL was closer to the expected value. According to the data, increasing bacteriocin activity required employing the ideal sucrose concentration, NaCl concentration, and incubation time. The partially purified bacteriocin was found stable at temperatures between 24 and 50 °C and at pH 5-8. The molecular weight purified bacteriocin was determined to be between 13 and 35 kDa.

Purification and characterization of a novel low-molecular-weight antimicrobial peptide produced by Lactiplantibacillus plantarum NMGL2

The present study aimed to purify and characterize a novel low-molecular-weight antimicrobial peptide (AMP) named as PNMGL2 produced by Lactiplantibacillus plantarum NMGL2. The AMP was effectively separated and purified by ethyl acetate extraction and DEAE-Sepharose anion exchange chromatography. Tricine-SDS-PAGE of the purified AMP showed a major protein band below 1.7 kDa, which was identified by MALDI-TOF MS to be a hexapeptide LNFLKK (761.95 Da), and structurally characterized to be combination of helixes and random coil by a PEP-FOLD 3 De novo approach. The antimicrobial activity of LNFLKK was confirmed by chemical synthesis of the peptide that showed clear inhibition (MIC 7.8 mg/mL) against both Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes), and Gram-negative bacteria (Enterobacter sakazakii, Escherichia coli and Shigella flexneri). PNMGL2 was pH resistant (pH 2-9), heat stable (121 °C, 30 min), and protease sensitive. Treatment of UV rays, sodium chloride and organic solvents did not decrease the activity. Sequencing of the whole genome of L. plantarum NMGL2 revealed presence of a bacteriocin gene cluster with two putative bacteriocin genes (ORF4 and ORF5) that were not expressed, confirming the significance of PNMGL2 contributing the antimicrobial activity of the strain. This study demonstrated the low-molecular-weight AMP that was uncharacterized in the relevant available databases, suggesting its potential application as a novel natural food preservative.

Antimicrobial Activity and Immunomodulatory Properties of Acidocin A, the Pediocin-like Bacteriocin with the Non-Canonical Structure

Pediocin-like bacteriocins are among the natural antimicrobial agents attracting attention as scaffolds for the development of a new generation of antibiotics. Acidocin A has significant structural differences from most other members of this subclass. We studied its antibacterial and cytotoxic activity, as well as effects on the permeability of E. coli membranes in comparison with avicin A, the typical pediocin-like bacteriocin. Acidocin A had a more marked tendency to form an alpha-helical structure upon contact with detergent micelles, as was shown by CD spectroscopy, and demonstrated considerably less specific mode of action: it inhibited growth of Gram-positive and Gram-negative strains, which were unsusceptible to avicin A, and disrupted the integrity of outer and inner membranes of E. coli. However, the peptide retained a low toxicity towards normal and tumor human cells. The effect of mutations in the pediocin box of acidocin A (on average, a 2-4-fold decrease in activity) was less pronounced than is usually observed for such peptides. Using multiplex analysis, we showed that acidocin A and avicin A modulated the expression level of a number of cytokines and growth factors in primary human monocytes. Acidocin A induced the production of a number of inflammatory mediators (IL-6, TNFα, MIG/CXCL9, MCP-1/CCL2, MCP-3/CCL7, and MIP-1β) and inhibited the production of some anti-inflammatory factors (IL-1RA, MDC/CCL22). We assumed that the activity of acidocin A and similar peptides produced by lactic acid bacteria might affect the functional state of the human intestinal tract, not only through direct inhibition of various groups of symbiotic and pathogenic bacteria, but also via immunomodulatory effects.

Structural Features, Mechanisms of Action, and Prospects for Practical Application of Class II Bacteriocins

Bacteriocins are antimicrobial peptides ribosomally synthesized by both Gram-negative and Gram-positive bacteria, as well as by archaea. Bacteriocins are usually active against phylogenetically related bacteria, providing competitive advantage to their producers in the natural bacterial environment. However, some bacteriocins are known to have a broader spectrum of antibacterial activity, including activity against multidrug-resistant bacterial strains. Multitude of bacteriocins studied to date are characterized by a wide variety of chemical structures and mechanisms of action. Existing classification systems for bacteriocins take into account structural features and biosynthetic pathways of bacteriocins, as well as the phylogenetic affiliation of their producing organisms. Heat-stable bacteriocins with molecular weight of less than 10 kDa from Gram-positive and Gram-negative producers are divided into post-translationally modified (class I) and unmodified peptides (class II). In recent years there has been an increasing interest in the class II bacteriocins as potential therapeutic agents that can help to combat antibiotic-resistant infections. Advantages of unmodified peptides are relative simplicity of their biotechnological production in heterologous systems and chemical synthesis. Potential for the combined use of bacteriocins with other antimicrobial agents allowing to enhance their efficacy, low probability of cross-resistance development, and ability of probiotic strains to produce bacteriocins in situ make them promising candidate compounds for creation of new drugs. The review focuses on structural diversity of the class II bacteriocins and their practical relevance.

Natural Compounds With Antimicrobial and Antiviral Effect and Nanocarriers Used for Their Transportation

Due to the increasing prevalence of life-threatening bacterial, fungal and viral infections and the ability of these human pathogens to develop resistance to current treatment strategies, there is a great need to find and develop new compunds to combat them. These molecules must have low toxicity, specific activity and high bioavailability. The most suitable compounds for this task are usually derived from natural sources (animal, plant or even microbial). In this review article, the latest and most promising natural compounds used to combat bacteria, filamentous fungi and viruses are presented and evaluated. These include plant extracts, essential oils, small antimicrobial peptides of animal origin, bacteriocins and various groups of plant compounds (triterpenoids; alkaloids; phenols; flavonoids) with antimicrobial and antiviral activity. Data are presented on the inhibitory activity of each natural antimicrobial substance and on the putative mechanism of action against bacterial and fungal strains. The results show that among the bioactive compounds studied, triterpenoids have significant inhibitory activity against coronaviruses, but flavonoids have also been shown to inhibit SARS-COV-2. The last chapter is devoted to nanocarriers used to improve stability, bioavailability, cellular uptake/internalization, pharmacokinetic profile and reduce toxicity of natural compunds. There are a number of nanocarriers such as liposomes, drug delivery microemulsion systems, nanocapsules, solid lipid nanoparticles, polymeric micelles, dendrimers, etc. However, some of the recent studies have focused on the incorporation of natural substances with antimicrobial/antiviral activity into polymeric nanoparticles, niosomes and silver nanoparticles (which have been shown to have intrinsic antimicrobial activity). The natural antimicrobials isolated from animals and microorganisms have been shown to have good inhibitory effect on a range of pathogens, however the plants remain the most prolific source. Even if the majority of the studies for the biological activity evaluation are in silico or in vitro, their internalization in the optimum nanocarriers represents the future of “green therapeutics” as shown by some of the recent work in the field.